Re: Sauropod Ancestors

[Stan Friesen <swf@ElSegundoCA.ATTGIS.COM>]

>From: Tom Holtz <tholtz@geochange.er.usgs.gov>
 > Concerning sauropod ancestors:
 > 
 > The recent claims that Prosauropoda is the sister-group, rather than a
 > paraphyletic stem group, of the Sauropoda basically hinges on a single
 > character, the fact that the fifth metatarsal of the foot is much more
 > reduced in prosauropods than in sauropods.  However, reversals happen (and
 > in fact, this particular reversal happens independantly in the origin of
 > the therizinosauroids), and one character taxa should always be held with
 > some reservation.

Another case where reversal needs to be seriously considered is
when the features involved are mostly continuous metric ones, especially
if they are size correlated.  (For instance, the early robust
australopithicine, KNM-WT 17000 I think, which is intermediate
in robustness between the two later morphs).

Now, if the toe were actually *lost*, the case might be different :-)
 > 
 > To my knowledge, no one has published an analysis (including data matrix)
 > for all sauropodomorphs [grad students looking for a major project, take
 > note!].  I suspect that, when one is run, the sauropods will fall among the
 > "melanorosaurids" sensu lato.

That would be my current best guess as well.
[Some of the earliest "true sauropods" are not really that different
from "melanorosaurids"].

With the plateosaurids and the thecodontosaurids as progressively
more distant groups.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.